Travelling with a mobile phone
The UK network uses the 900 or 1800 GSM system, so visitors from the United States (where the system is 800 or 1900 MHz band) will need to acquire a tri- or quad-band set. Contact your service provider for specific details.
You may need to inform your network operator in advance of your trip so the “roaming” facility can be enabled. When abroad, you will be charged for the calls you receive, as well as for the calls you make; in addition, you have to pay a substantial premium for the international leg of the call.
It is easier and cheaper to purchase a SIM card locally and top it up with credit. This will allow you to use the local mobile-phone networks, though you can only do this if your handset is not locked to a specific network.
Alternatively, you could buy a new phone and top up with a pay-as-you-go card. Make sure the phone you buy can accept international calls. Check that your insurance policy covers you in case your phone gets stolen, and keep your network operator’s helpline number handy for emergencies.